Ed Sheeran has revealed that his upcoming album – (Subtract) was inspired by a series of personal tragedies that he faced last year, including his wife’s tumour diagnosis and his friend’s sudden death.

The singer-songwriter, who is currently in a US court defending himself against a copyright infringement claim over his hit song Thinking Out Loud, said that he “spiralled” into depression and anxiety after learning that his childhood sweetheart Cherry Seaborn had developed a tumour while pregnant with their second child.

“There was no route to treatment until after the birth,” he wrote in a handwritten note posted on social media. “It changed my life, my mental health, and ultimately the way I viewed music.”

He also said that he was devastated by the loss of his best friend Jamal Edwards, who died aged 31 after taking cocaine and drinking alcohol. Edwards was the founder of SBTV, an online platform that gave Sheeran his first big break.

“I felt like I was drowning, head below the surface, looking up but not being able to break through for air,” he said. “I wrote without thought of what the songs would be, I just wrote whatever tumbled out. And in just over a week, I replaced a decade’s worth of work with my deepest, darkest thoughts.”

The result is – (Subtract), an acoustic album produced by Aaron Dessner of The National, which Sheeran described as “opening the trapdoor into my soul”. The album is due for release on 5 May, with Sheeran playing a handful of shows in Europe to debut the first single at the end of March.

The album is the final instalment of his “mathematical era”, which began with + (Plus) in 2011 and continued with x (Multiply), ÷ (Divide), and = (Equals). But unlike his previous records, which featured a variety of genres and collaborations, – (Subtract) focuses on a single, melancholy sound.

“For the first time I’m not trying to craft an album people will like, I’m merely putting something out that’s honest and true to where I am in my adult life,” he said.

Sheeran did not provide an update on his wife’s health or their second daughter, who was born last May. He also did not comment on the outcome of his US trial, which may arrive on Subtract’s release date. He is accused of copying an ascending four-chord sequence and its rhythm from Marvin Gaye’s 1973 hit Let’s Get It On for his 2014 single Thinking Out Loud.

The lawsuit is being brought by the heirs of Gaye’s co-writer on Let’s Get It On, Ed Townsend, who claim that Sheeran and co-writer Amy Wadge infringed on their copyright. Sheeran has denied the allegations and argued that many songs are written on the same chord progressions.

Sheeran has previously faced similar claims over his songs Shape Of You and Photograph, but he won both cases in the UK.